1. Field of the Invention
The present invention relates to a method for inkjet textile printing wherein an aqueous pigment ink is inkjet-printed on a textile fiber product after pretreatment and a textile fiber product prepared using the method.
2. Description of the Prior Art
In recent years, inkjet textile printing with an ink containing a dye or pigment as a colorant has been developed as a method of coloring a textile fiber product with the advantage of obviation of the need for plate making.
In the case of coloring with a dye, a textile fiber product, pretreated with a cellulose thickener or the like in advance, is then inkjet-printed with an ink containing a dye suitable for the kind of fiber as a colorant. Accordingly, inks containing reactive dyes or direct dyes for cellulose fibers such as cotton or hemp, acid dyes for animal fibers such as wool or silk, acid dyes or disperse dyes for nylon fibers, disperse dyes for polyester fibers, and cationic dyes for acrylic fibers, are used as colorants respectively. After inkjet printing, steps for steaming, washing, soaping, drying and so on are taken to yield a textile fiber product with desired pattern without plate making.
However, because a dye is used as a colorant, it is necessary to change the dye (hence the ink containing the dye) according to the kind of fiber, and problems arise from the complex processes following inkjet printing, such as for steaming, washing, soaping, and drying, and a tendency for increasing environmental load.
Meanwhile, in the case of coloring with an ink containing a pigment, which, unlike dyes, is a colorant that does not have substantivity for fibers, there are advantages in that unlike dyes, textile fiber products of various fibers can be colored with a single kind of ink, and that the environmental load is low because of the obviation of the need for steaming and washing steps after printing, although a binder is needed to bind the pigment to the fiber.
However, because pigments, unlike dyes, occur as insoluble color-imparting particles, inkjet printing using a pigment ink poses the problems of clogging in the fine nozzle of inkjet printing machine and the possible occurrence of time-related precipitation and flocculation of the pigment in the ink. The same poses other problems, including a tendency for film formation on the nozzle tip of inkjet printing machine and hence nozzle clogging caused by the binder needed to bind the pigment to the fiber, a tendency toward a hard feeling, and difficulty in obtaining sufficient fastness. Still another problem can arise when a pigment ink is printed directly on fiber: the pigment ink penetrates the fiber, making it difficult to obtain high-density patterns, and the pigment ink undergoes migration, making it difficult to obtain brilliant images.
Examples of past proposals concerning color impartment by an inkjet process using a pigment as a colorant include the techniques described in the references (1) to (6) below.
(1) JP-A-2003-268271
A technique for performing inkjet textile printing with excellent performance in printing stability, discharge stability, storage stability, and washing fastness by dispersing a pigment using an organic polymer compound having an anionic group, previously polymerized in a solvent, thereafter distilling off the solvent, adding an acid for acid deposition to cover the pigment surface with the organic polymer compound, and thereafter heating a fabric inkjet-printed using an ink prepared by blending a block isocyanate in a colorant solubilized by the addition of water and a base.
(2) JP-A-2009-215506
A technique for using a ink for inkjet textile printing to print a fabric comprising a pigment, a water-dispersible resin, a block isocyanate compound as a crosslinking agent, and water, and exhibiting good performance in color fastness to washing and rubbing.
(3) JP-A-2006-218791
A technique for using an inkjet recording material that exhibits excellent performance in image brilliancy, water resistance, light resistance, and chromogenicity, comprising a polylactic acid fiber base and an ink receiving layer formed thereon, the layer comprising an aqueous emulsion type acrylic adhesive having a glass transition point ranging from −50° C. to −10° C. and a water-soluble cationic polymer as primary components.
(4) JP-A-2009-215686
A method for inkjet textile printing having both high color fastness to rubbing and excellent chromogenicity and brilliancy, comprising pretreating a fabric with a water dispersion of a cationic polymer, thereafter coloring the fabric by inkjet, then post-treating with a dispersion of a block isocyanate in water, and heating at 120° C. to 210° C.
(5) JP-T-2010-503779
A method for digital printing of a fabric, comprising    (a) a step for pretreating the fabric with an aqueous pretreatment solution containing a nonionic latex polymer and a polyvalent cation salt solution,    (b) a step for drying the pretreated fabric, and    (c) a step for digital printing the dry pretreated fabric with a color inkjet ink,wherein the nonionic latex polymer has a sufficient nonionic component to make it stable in the presence of the polyvalent cation salt solution.
(6) JP-A-HEI-11-315485
A technique concerning an inkjet-printed fabric having (a) an aqueous ink comprising an aqueous vehicle and a colorant and (b) a fabric to be printed with the aqueous ink, wherein the fabric has been treated with a hydrophilic composition containing at least one kind of crosslinkable thermoplastic polymer having a molecular weight of at least 6000, and selected from the group consisting of (1) a polymer having at least one carboxylic acid group and at least one crosslinkable group and (2) a polymer selected from the group consisting of mixtures of a first polymer having at least one carboxylic acid group and a second polymer having at least one crosslinkable group.
However, the proposals described in the aforementioned references (1) to (6) are problematic in the aspects shown below.
The technique described in the reference (1) cannot be said to be an appropriate method of obtaining a colorant because it requires the complex steps of once finely dispersing a pigment in a solvent system, then performing acid deposition to bind an organic polymer compound to the pigment surface, and thereafter blending a base to solubilize the pigment to obtain a colorant, its workability is low, and its process is painstaking. In addition, the pigment dispersion prepared by dispersing a pigment using such a pigment-dispersing agent is highly viscous, and when the pigment is dispersed to high density, the ink viscosity increases to the extent that the ink cannot be used for inkjet; therefore, the pigment dispersion is not considered to be suitable for an inkjet ink of high color density. In addition, when a fabric is colored with this ink formulated with a block isocyanate and subjected to a heat treatment, the bindability of the ink component to the fabric is weak, and it is unlikely that satisfactory fastness is obtained.
In the technique described in the reference (2), like the technique described in the reference (1), a block isocyanate compound is formulated as a crosslinking agent in a coloring ink only, and the crosslinking of the water-dispersible resin and block isocyanate compound in the coloring ink alone does not cause sufficient pigment binding to the fabric; therefore, this technique is not considered to ensure adequate fastness.
In the technique described in the reference (3), a fiber base is pretreated with a composition of an aqueous emulsion type acrylic adhesive and a water-soluble cationic polymer as the primary components in advance to cover the entire surface of the fiber base with a resin film; therefore, it is thought that the feeling of the fiber base hardens, and that the breathability is adversely affected. In addition, because inkjet printing is performed on a hydrophobic film, it is thought that brilliant images are difficult to obtain due to ink repellency.
The technique described in the reference (4) is intended to improve the fastness by pretreating a fabric with a cationic polymer to increase the color development density of inkjet prints, and post-treating the fabric with a block isocyanate compound; however, pretreatment with the polymer hardens the feeling. In addition, when inkjet printing is followed by a post-treatment with a block isocyanate, crosslinking of the binder and block isocyanate in the coloring ink occurs, improving the water resistance of the binder; however, the binding of the fabric and the pigment and binder is insufficient; therefore, this technique is not considered to ensure adequate fastness for a colored fabric.
The techniques described in the references (5) and (6), like the technique described in the reference (4), are considered to adversely affect the feeling because of pretreatment of the fabric with a polymer, and to make it difficult to obtain brilliant images due to ink repellency because of inkjet printing on a hydrophobic film.
As stated above, when using a dye as a colorant in coloring a textile fiber product by an inkjet process, clogging in the nozzle of inkjet apparatus is unlikely to occur, the ink discharge stability is good, and with dyeing affinity for fiber, the quality properties such as feeling and fastness of the colored textile fiber product are good. In this case, however, it is necessary to choose a dye according to the kind of fiber, and moreover, problems arise from the complex steps that cannot be said to be efficient, the cost requirements for equipment and resource consumption, and the relatively high environmental load by waste liquid.
Meanwhile, when using a pigment as a colorant in coloring a textile fiber product by an inkjet process, it is unnecessary to choose a pigment according to the kind of fiber, and the steps are relatively simple; however, this method poses problems concerning the long-term storage stability of the pigment ink, possible occurrence of clogging in the nozzle of inkjet apparatus and discharge stability reduction, and difficulty in obtaining good quality properties such as feeling and fastness of the colored textile fiber product.
For this reason, there is a demand for the development of a method of coloring a textile fiber product by an inkjet process using an ink containing a pigment as a colorant, which method enables the obtainment of brilliant images and a colored product with excellent color fastness and soft feeling while preventing clogging in the fine nozzle of inkjet printing machine.